1. Field of the Invention
The present invention relates to an improved video display device to display a color video by spatially modulating light obtained by adding red color light, green color light, and blue color light, or light obtained by adding white color light in addition to light obtained by adding the red color light, the green color light, and the blue color light.
The present application claims priority of Japanese Patent Application No. 2002-241241 filed on Aug. 21, 2002, which is hereby incorporated by reference.
2. Description of the Related Art
Conventionally, a method for displaying a color video by spatially modulating each of red color light, green color light, and blue color light and by synthesizing them is known. FIG. 11 is a schematic block diagram showing an example of circuit configurations of a conventional spatial modulating-type video display device as disclosed in, for example, Japanese Patent Application Laid-open No. Hei 10-269802.
The conventional video display device chiefly includes a red color light source 111, a green color light source 112, a blue color light source 113, spatial light modulators 116, 117, and 118, an image synthesis optical system 119, a red color light source driving circuit 121, a green color light source driving circuit 122, a blue color light source driving circuit 123, a red spatial light modulator driving circuit 131, a green spatial light modulator driving circuit 132, a blue spatial light modulator driving circuit 133, a red image memory 151, a green image memory 152, a blue image memory 153, a video signal processing circuit 154, and a timing control circuit 161.
First, operations of optical systems in the conventional video display device are described by referring to FIG. 11. The spatial light modulator 116 for the red color performs spatial light modulation on red color light being incident from the red color light source 111 and emits red color image light, The spatial light modulator 117 for the green color performs spatial light modulation on green color light being incident from the green color light source 112 and emits green color image light. The spatial light modulator 118 for the blue color performs spatial light modulation on blue light being incident from the blue color light source 113 and emits blue color image light. The image synthesis optical system 119 performs image synthesis on the incident red color image light, the incident green color image light, and the incident blue image color light and emits synthesized image light. The emitted synthesized image light is projected through a projection optical system (not shown) onto a screen (not shown).
Next, configurations of circuits of the conventional video display device are explained by referring to FIG. 11. Each of the red color light source driving circuit 121, the green color light source driving circuit 122, and the blue color light source driving circuit 123 drives each of the red color light source 111, the green color light source 112, and the blue color light source 113. Each of the red spatial light modulator driving circuit 131, the green spatial light modulator driving circuit 132, and the blue spatial light modulator driving circuit 133 drives each of the spatial light modulators 116, 117, and 118, according to a video signal for a red color, for a green color, and for a blue color, respectively. The timing control circuit 161 controls operational timing of each of the video signal processing circuit 154, the red spatial light modulator driving circuit 131, the green spatial light modulator driving circuit 132, and the blue spatial light modulator driving circuit 133 according to an input video signal 101.
The video signal processing circuit 154 performs video signal processing such as sync detection, color space conversion, degamma correction, or a like on the input video signal 101 and produces a video signal for each of the red color, the green color, and the blue color. Moreover, the video signal processing circuit 154 accumulates the produced video signals for the red, the green and the blue colors in the red image memory 151, the green image memory 152, and the blue image memory 153, respectively, and reads these signals from these memories, the red image memory 151, the green image memory 152, and the blue image memory 153.
FIG. 12 shows control timing for each component in the conventional video display device. Each of the red color light source 111, the green color light source 112, and the blue color light source 113 ordinarily is put in a driven and light-emitted state. Each of video signals to drive each of the spatial light modulators 116, 117, and 118 is renewed in every frame period. A video signal for a red color drives the spatial light modulator 116 for a red color. A video signal for a green color drives the spatial light modulator 117 for a green color. A video signal for a blue color drives the spatial light modulator 118 for a blue color.
Next, a conventional method for making image brighter in a conventional video display device is described. Conventionally, in order to display a color video, a method is employed in which each pixel making up a screen is divided into sub-pixels each producing each of three primary colors consisting of red (R), green (G), and blue (B) colors so that brightness in each of the sub-pixels is controlled and so that images produced by the sub-pixels is recognized visually as a color image. However, in terms of the brightness, if a screen is not sufficiently bright in a viewing environment, the image is difficult to see clearly. To solve this problem, a method is proposed in which the brightness is given to an entire image by adding a white color (W) as a color component to obtain a more vivid color video.
As an example of the video display device employing such the method as described above, a liquid crystal display device serving as a direct-view-type video display device is disclosed in, for example, Japanese Patent Application Laid-open No. 2002-149116, in which a screen that can provide proper luminance can be displayed by incorporating a sub-pixel for a white color (w), in addition to sub-pixels for red (R), green (G), and blue (B) colors, all making up each pixel in a liquid crystal panel, by calculating output luminance data for the white color from input data for the R, the G, and the B colors using a decoder, and by simultaneously driving all the sub-pixels for each of the red (R), the green (G), the blue (B), and the white (W) colors using the obtained luminance data together with the input data for the R, the G, and the B colors.
In the case of a projector to project a color video onto a screen, a color-sequence-method is generally employed in which, by sequentially applying light of three colors of red (R), green (G), and blue (B) colors to a spatial light modulator in which transmittance or reflectance is controlled spatially according to a video signal, an image of each color to be projected through the spatial light modulator onto the screen is recognized as a color video in a visually mixed state.
Human eyes have a capability of integration with a time constant of being several tens of milliseconds and, since a frame period during which an image consisting of red video light, green video light, and blue video light, all being emitted from the spatial light modulator, is switched, that is, a frame period of a video signal is ordinarily shorter than integral time constant of human eyes, when an image having a color being different in every frame period, while being sequentially switched according to a lapse of time, is projected, the human eyes recognize the image as a color image.
Next, configurations of a conventional color-sequence-type and spatial light modulating type are described. FIG. 13 is a schematic block diagram showing configurations of an optical system in the conventional color-sequence-type video display device as disclosed in, for example, Japanese Patent Application Laid-open No. Hei 10-269802.
The optical system of the above conventional color-sequence-type video display device chiefly includes a light source section 100, being made up of a red color light source 111, a green color light source 112, and a blue color light source 113, and an image synthesis optical system 115, and a spatial light modulator 130.
As shown in FIG. 13, the red color light source 111 emits red color light. The green color light source 112 emits green color light. The blue color light source 113 emits blue color light. The image synthesis optical system 115 synthesizes the red color light incident from the red light source 111, the green color light incident from the green light source 112, and the blue color light incident from the-blue light source 113 and sequentially emits the light to a same optical path. The spatial light modulator 130 performs spatial light modulation on the light emitted from the image synthesis optical system 115 sequentially and outputs the light.
The color synthesis optical system 15 to perform synthesis of red color light, green color light, and blue color light fed from each of the light sources can be made up of a dichroic prism, a dichroic mirror, polarization unifying units, fly-eye lens or a like. To reduce shading of light to be applied to the spatial light modulator 30, an optical integrator may be employed.
An example of a color synthesis optical system using a dichroic prism is disclosed in, for example, Japanese Patent Application Laid-open No. 2000-56410. An example of a color synthesis optical system using a dichroic mirror is disclosed in, for example, Japanese Patent Application Laid-open No. Hei 8-240779. An example of a color synthesis optical system using a fly-eye lens is disclosed in, for example, Japanese Patent Application Laid-open No. Hei 11-2278 and Japanese Patent Application Laid-open No. 2001-343706. An example of a color synthesis optical system having a configuration to reduce shading of light by using an optical integrator is disclosed in, for example, for example, Japanese Patent Application Laid-open No. Hei 10-269802. Moreover, the polarization unifying unit can be realized by such a method as disclosed in Japanese Patent Application Laid-open No. Hei 6-289387.
In the video display device shown in FIG. 13, the red color light, the green color light, and the blue color light emitted from the red color light source 111, the green color light source 112, and the blue color light source 113 are synthesized by the image synthesis optical system 115 and the synthesized color light is emitted to a same optical path. In the spatial light modulator 130, transmittance of light is spatially controlled according to a spatial light modulator driving signal and light incident from the image synthesis optical system 115 is spatially modulated sequentially and is emitted. Thus, red image light, green image light, and blue image light emitted from the spatial light modulator 130 are sequentially projected through a projection optical system (not shown) onto a screen and forms a color image.
Next, operations of controlling a light source for each color in the conventional video display device shown in FIG. 13 is described. The spatial light modulator driving signal is fed to the spatial light modulator 130. The spatial light modulator driving signals, as shown in FIG. 14, include a video signal for a red color (R-video), a video signal for a green color (G-video), and a video signal for a blue color (B-video), which are sequentially input to the spatial light modulator 130.
While the video signal for the red color is being fed to the spatial light modulator 130, red color light is input to the image synthesis optical system 115. While the video signal for the green color is being fed to the spatial light modulator 130, green color light is input to the image synthesis optical system 115. While the video signal for the blue color is being fed to the spatial light modulator 130, the blue color light is input to the image synthesis optical system 115. Since each of the red color light, the green color light and the blue color light is sequentially input through the image synthesis optical system 115 to the spatial light modulator 130, red color image light, green color image light, and blue color image light are sequentially emitted as image light from the spatial light modulator 130, projected onto the screen and recognized as a color video.
In the case of the color-sequence-type video display device, by adding a white (W) color as a color component to give brightness to an entire image, it is possible to obtain a more visible color image. A conventional color-sequence-type video display device is already provided in which brightness is given to an entire image by adding time required for applying white color light to sequence of applying each of the R, the G, and the B color light to the spatial light modulator, as disclosed in, for example, Japanese Patent Application Laid-open No. Hei 11-102170, Japanese Patent Application Laid-open No. 2001-184037, and Japanese Patent Application Laid-open No. 2002-82652.
In the above conventional video display devices, there are two methods of producing each of the R, the G, the B, and the W color light to be applied to the spatial light modulator. According to one method, each of the R, the G, the B, and the W color light is produced by using a rotary-type color filter plate (color wheel) which can emit each of the R, the G, and the B color light in its filter region for each of the R, the G, and the B colors and by introducing a region for the W color among filter regions for the R, the G, and the B colors to emit the W color light. According to another method, each of the R, the C, the S, and the W color light is produced by using three kinds of optical devices (for example, liquid crystal color filters) each corresponding to each of the R, the G, and the B colors to emit each of the R, the G, and the B color light in every allocated period and by using an optical device which can emit the W color light or by introducing a period during which the W color light is emitted after having transmitted through each of the three kinds of optical devices corresponding to the R, the G, and the B colors.
As a video display device having been conventionally used, a CRT (Cathode Ray Tube) is known. In the CRT, a phosphor is excited by an electron beam emitted from an electron gun, and thus red color light, green color light, and blue color light are emitted from the phosphor in an excited state. At this point, luminance on a surface of the phosphor is controlled so as to be approximately proportional to current density of the electron beam and so that current density of an electron beam is proportional to a tone component of a video signal.
Three primary colors to be provided by the CRT consist of colors emitted from each phosphor for each of the three colors and colors are reproduced by performing an additive color mixture process on each of the emitted colors at a rate corresponding to a video signal. Specifications of colorimetry for color reproductivity of a CRT are designated by ITU (International Telecommunication Union Radiocommunication Sector)-R Rec. BT. 1361 and, when a video signal defined by specifications of colorimetry is projected by the CRT, a color video of an expected color is reproduced. However, in the case of a video display device in which each of the three primary colors has different chromaticity coordinates, a tint of a video (picture) becomes different.
Also, in the case of a video display device to display a video by spatially modulating light fed from each of red, green, and blue light sources, a semiconductor light emitting device or a like is used as a light source. However, since a light emitting principle of a semiconductor light emitting device is different from that of a CRT, it is difficult to make chromaticity coordinates of each of the three primary colors be exactly the same as designated by specifications in the ITU-R Rec. BT. 1361 described above and, therefore, the color reproductivity is different from that of the CRT. To solve this problem, conventionally, a method for calibrating colors is employed in which balance of brightness of light from a light source for each of the three primary colors (R, G, B) is simply adjusted so that a white point satisfies the specifications.
However, though this method can make tint the same regarding a white point, it is difficult to correct color reproductivity of a color having high excitation purity, that is, a vivid color. Thus, the conventional video display device employing the semiconductor light emitting device has a problem in that its color reproductivity is not sufficient.
Furthermore, the conventional color-sequence-type video display device has also a problem in that, in addition to a period for applying each of R, G, and B color light, an additional period for applying W color light is prepared separately. However, control on a spatial light modulator using a video signal for a white color during a period of applying W color light is required, which causes complicated circuits and impairs high-speed operations.